This invention relates generally to the packaging of semiconductors. More particularly, this invention relates to a technique for packaging a semiconductor to improve thermal cycling performance.
Semiconductors are placed in packages and are then subjected to a variety of electrical and thermal tests. The thermal tests typically entail exposing the package to a series of low and high temperatures, referred to as thermal cycles. For example, it is common to expect a packaged semiconductor to withstand at least 1000 thermal cycles between 1 and 100xc2x0 C. Additional thermal cycles typically cause damage to the semiconductor. This damage arises largely from the mechanical stress placed on the semiconductor. This mechanical stress stems from the mismatch in the thermal coefficients of expansion between the semiconductor, the substrate upon which it is mounted, and the epoxy bonding it to the substrate.
In view of the foregoing, it would be highly desirable to improve the thermal cycling performance of packaged semiconductors. Preferably, the technique would be low cost and would rely upon known packaging techniques.
The method of the invention is a process for packaging a semiconductor. The method includes dispensing a substrate epoxy onto a packaging substrate. A semiconductor epoxy is then applied to a semiconductor. The substrate epoxy is then engaged with the semiconductor epoxy.
A semiconductor package of the invention includes a relatively thin substrate epoxy attached to a packaging substrate, such as a lead frame. A relatively thick semiconductor epoxy is attached to a semiconductor. The relatively thin substrate epoxy and the relatively thick semiconductor epoxy are attached to one another, forming a stack including the packaging substrate, the relatively thin substrate epoxy, the relatively thick semiconductor epoxy, and the semiconductor. A housing encloses the stack.
The relatively thick semiconductor epoxy forms a compliant interface that reduces the stress imposed upon the semiconductor during thermal cycling. Thus, the package of the invention leads to extended semiconductor life. The relatively thick semiconductor epoxy is easily applied to the semiconductor in a separate process using standard techniques, such as spinning. Advantageously, the substrate epoxy may be applied to the substrate in accordance with prior art techniques, thereby preventing any alteration in prior art package assembly techniques. The substrate epoxy provides adhesion to the semiconductor epoxy, which may be in a cured state. Since the invention relies upon known packaging techniques, the invention can be implemented relatively easily at low cost.